The present invention relates to containers and the manufacture thereof and, more particularly, relates to an improved flexible container for bulk materials and an improved method of manufacturing the same.
The prior art includes systems of handling bulk materials utilizing a flexible receptacle having a large capacity. Such receptacles have, in the past, utilized an outer protective covering of flexible sheet material which can be doubled for additional strength. In one known receptacle, a double walled interior bag is provided, and a high strength filament is wound in a helix about the exterior surface of the double walled bag. A non-curing mastic adhesive is used to secure the filament to the double walled bag, and a sling of flexible webbing is used to support the receptacle. The bottom of the bag is formed by gathering and tying the bag to close one end, and a sling is used to support the bag which includes a plurality of concentric rings positioned below and supporting the receptacle. Straps connect the concentric rings and are used to lift and support the receptacle.
A method for manufacturing such a flexible receptacle is disclosed in U.S. Pat. No. 3,962,959; filed Dec. 16, 1974; and issued June 15, 1976; whereby one edge of a length of flexible sheet material is affixed to a mandrel, and the mandrel is rotated to wrap the sheet material about the mandrel. An adhesive is applied to the exterior of the sheet material, and the mandrel is rotated again to wrap a second sheet of material about the mandrel to form a second cylindrical wall. One end of the double walled cylinder, thus formed, is gathered and tied to form a closed end. An adhesive material is then applied to the exterior wall of the double walled cylinder, and a filament is wound in a helix about the second wall. A sling is positioned over the helically wound filament, and an outer cover sheet is adhesively attached around the exterior of the sling and the helically wound filament. Although such receptacles and methods for making the same have been adequate, they typically have required substantial amounts of labor in manufacturing. Manufacturing techniques were often slow and required hand labor. Therefore, according to one feature of the present invention, an improved method for making a receptacle results in faster and easier production, as well as providing a relatively inexpensive flexible receptacle for bulk materials of outstanding quality.
In accordance with the present invention, a reinforced receptacle for containing bulk materials includes a coextruded plastic multiple-ply tube having at least an inner and an outer ply and having an upper and a lower end. A reinforced sheet is wrapped around the multiple-ply tube and encompasses the tube from the lower end to the height to which the receptacle is filled with bulk materials. The reinforcing sheet includes a plurality of reinforcing filaments disposed circumferentially about and reinforcing the multiple-ply tube to prevent bursting and tearing of the multiple-ply tube when filled with bulk materials. The reinforcing sheet also includes a leading edge and a following edge with the leading edge overlapping and adhesively secured to the following edge to form a closed reinforcing belt or cylinder about the multiple-ply tube.
The lower end of the multiple-ply cylinder is folded and adhesively secured together to form a closed lower end, and the upper end of the multiple-ply tube extends above the reinforced sheet and above the bulk materials contained within the receptacle for a sufficient distance, so that the upper end may be gathered, clamped and used to lift the reinforced receptacle.
The folded bottom of the multiple-ply tube is folded to form a satchel bottom in the receptacle. Opposing lateral sides of the bottom end of the receptacle are folded inwardly, one towards the other. Then, the remaining front and rear opposing sides are folded inwardly, one towards the other, in a direction perpendicular to the fold direction of the first lateral opposing sides. Glue is applied between the overlapping surfaces of the folded material to adhesively secure the bottom of the multiple-ply tube in the folded satchel configuration.
In the preferred method of manufacturing the reinforced receptacle for bulk material, a plastic multiple-ply tube is coextruded and positioned in a flat position to form a flat collapsed tube. Two plastic sheets are formed having a length exceeding the circumference of the multiple-ply tube by a specified amount, and a plurality of substantially parallel filaments are positioned between the two plastic sheets extending along the length of the sheets. The two plastic sheets are adhesively secured together with the parallel filaments adhesively secured between the sheets forming a multiple-ply reinforced sheet. An adhesive is applied to the midregion of the multiple-ply tube, and the reinforced sheet is wrapped and adhesively secured about the midregion of the flat, collapsed, multiple-ply tube with the filaments disposed concentrically and leaving an upper and lower portion of the multiple-ply tube extending beyond the reinforced sheet. A leading edge of the reinforced sheet is overlapped and adhesively secured to the trailing edge of the reinforced sheet to form a closed reinforcing collapsed cylinder about the flat tube.
The lower portion of the multiple-ply tube extending beyond the reinforced sheet is folded and glued together to form a folded satchel bottom on the receptacle. Folding and adhesively securing together one end of the multiple-ply tube eliminates the knot of material formed when the end of a receptacle is gathered and tied, as well as providing a reliable, inexpensive means of closing one end of the receptacle.
When the reinforced receptacle is filled with bulk materials, the upper portion of the multiple-ply tube is gathered and clamped by a clamp means that uniformly distributes the clamping force on the upper portion. A lifting force applied through the clamp means is uniformly distributed about the circumference of the multiple-ply tube to lift without tearing the receptacle.
In accordance with another embodiment of the present invention, a reinforced polyethylene two-ply receptacle is manufactured by coextruding a polyethylene two-ply cylinder having inner and outer cylindrical walls. The two-ply cylinder is positioned on a mandrel leaving a portion of the two-ply cylinder having a length greater than the radius of the mandrel overhanging the end of the mandrel. This overhanging portion of the two-ply cylinder is folded and adhesively secured together to form a satchel bottom to close one end of the two-ply cylinder. The mandrel is rotated, and a mastic is applied to the exterior of the two-ply cylinder. A reinforcing sheet having concentrically disposed filaments is wrapped about the two-ply cylinder. The trailing edge of the reinforcing sheet is overlapped and adhesively secured to the leading edge of the polyester sheet. While the mandrel is again rotated, mastic material is applied to the exterior of the reinforcing sheet, and a cover sheet of polyethylene is wrapped about the reinforcing sheet to prevent damage by abrasion. The two-ply cylinder is then removed from the mandrel.